Safety switch

Abstract

A safety switch plunger includes a moveable conductor which extends transversely through the plunger and protrudes from opposite sides of the plunger. The plunger is provided with a structure that is positionally fixed on the plunger. The structure is positioned such that it is arranged to come into physical contact with and affect the movement of the moveable conductor when the moveable conductor and plunger are moved relative to one another thereby providing a fail-to-safe safety switch.

1. A plunger of a safety switch comprising:
 a moveable conductor which extends transversely through the plunger and protrudes from opposite sides of the plunger; and wherein 
 the plunger is also provided with a structure that is fixed in position on the plunger, the structure extending in a radially outward direction from the plunger to overlap an area associated with movable conducting engagement of the moveable conductor and being positioned such that it is arranged to come into physical contact with and affect movement of the moveable conductor when the moveable conductor and plunger are moved relative to one another by a predetermined amount. 
 
     
     
       2. The safety switch plunger as claimed in  claim 1 , wherein the structure is arranged to cause the moveable conductor to one of rotate or pivot when the moveable conductor and plunger are moved relative to one another by the predetermined amount. 
     
     
       3. The safety switch plunger as claimed in  claim 1 , wherein the structure is a frame which extends away from the plunger to overlap one side of the moveable conductor with respect to the opposite sides of the plunger. 
     
     
       4. The safety switch plunger as claimed in  claim 3 , wherein the frame extends perpendicularly away from the plunger. 
     
     
       5. The safety switch plunger as claimed in  claim 3 , wherein the frame defines three sides of a rectangle. 
     
     
       6. The safety switch plunger as claimed in  claim 1 , wherein the structure comprises an arm which extends away from the plunger, the arm being provided with a hook at an end of the arm remote from the plunger. 
     
     
       7. The safety switch plunger as claimed in  claim 1 , further comprising a lip extending from one of the moveable conductor and an insulating barrier of the moveable conductor, the lip being arranged to come into physical contact with the structure when the moveable conductor and the plunger are moved relative to one another by the predetermined amount. 
     
     
       8. The safety switch plunger as claimed in  claim 7 , wherein the lip one of extends away from the plunger and extends generally perpendicularly away from the plunger. 
     
     
       9. A safety switch comprising:
 a housing; 
 a fixed conductor located within the housing and fixed in position relative to the housing; 
 a plunger, axially moveable within the housing and provided with a moveable conductor which extends transversely through the plunger and protrudes from opposite sides of the plunger; 
 a biasing element, arranged to bias the plunger into contact with a cam arrangement and arranged to bias the plunger such that the moveable conductor of the plunger is biased toward and into electrical connection with the fixed conductor, the cam arrangement being configured such that rotation of the cam arrangement will allow the plunger to move and to bring the moveable conductor of the plunger into electrical connection with the fixed conductor of the housing; and wherein 
 the plunger is provided with a structure that is fixed in position on the plunger, the structure being positioned such that it is arranged to extend in a radially outward direction from an elongated body of the plunger and generally along a backside of the moveably conductor and come into physical contact with and affect movement of the moveable conductor when the moveable conductor and plunger are moved relative to one another by a predetermined amount, such that at least a part of the moveable conductor is moved out of electrical connection with the fixed conductor, so that the safety switch is incapable of conducting electricity. 
 
     
     
       10. The safety switch as claimed in  claim 9 , wherein the predetermined amount of relative movement corresponds to a movement of the plunger due to a failure of the cam arrangement. 
     
     
       11. The safety switch as claimed in  claim 9 , wherein the structure is arranged to cause the moveable conductor to one of rotate or pivot when the moveable conductor and plunger are moved relative to one another by the predetermined amount. 
     
     
       12. The safety switch as claimed in  claim 9 , wherein the structure is arranged to cause the moveable conductor to one of rotate or pivot about the fixed conductor. 
     
     
       13. The safety switch as claimed in  claim 9 , wherein the structure is a frame which extends away from the plunger in a direction of one of the opposite sides of the plunger. 
     
     
       14. The safety switch as claimed in  claim 13 , wherein the frame extends perpendicularly away from the plunger. 
     
     
       15. The safety switch as claimed in  claim 13 , wherein the frame defines three sides of a rectangle. 
     
     
       16. The safety switch as claimed in  claim 9 , wherein the structure comprises an arm which extends away from the plunger, the arm being provided with a hook at an end of the arm remote from the plunger. 
     
     
       17. The safety switch as claimed in any of  claim 10 , further comprising a lip extending from one of the moveable conductor and an insulating barrier of the moveable conductor, the lip being arranged to come into physical contact with the structure when the moveable conductor and plunger are moved relative to one another by the predetermined amount. 
     
     
       18. The safety switch as claimed in  claim 17 , wherein the lip extends one of away from the plunger or generally perpendicularly away from the plunger. 
     
     
       19. A safety switch assembly comprising:
 a set of fixed contacts; 
 a set of moveable contacts; 
 a plunger constructed to move the moveable contacts relative to the fixed contacts such that the fixed contacts and moveable contacts can be separated; 
 a structure extending from the plunger and constructed to engage the contacts such that a first group of contacts including a fixed contact and a moveable contact are biased together and a second group of contacts including another fixed contact and another moveable contact are biased apart thereby severing electrical connectivity between the set of fixed contacts and the set of moveable contacts; and 
 wherein the structure extends in a radially outward direction from the plunger so as to extend into an area that overlies a contact area of the set of fixed contacts and the set of movable contacts along a side of the moveable contact that does not face the fixed contact. 
 
     
     
       20. The safety switch assembly of  claim 19  wherein the moveable contact of the second group of contacts is rotatable about the first group of contacts such that the second group of contacts maintains an open electrical condition when the structure engages the contacts.